In Windows Server 2003 several administrators where able to connect over RDP to a server by using same user account. It was nice, because couple of us where able to do several things at once and speed up the process.
But, in Windows server 2008, by default, you can not use same username to create multiple RDP connections to the same server. What you need to do is modify local or group policy for that server. Open gpedit.msc (if editing local policy) and in Computer Configuration locate Administrative Templates\Windows Components\Terminal Services\Terminal Server\Connections\ key and edit "Restrict each user to a single session" setting to Disabled. And that is it. 🙂